Air diffusers are well known which provide a plenum chamber above the ceiling from which air discharges into a room through suitable openings in the ceiling. Such known diffusers require an air deflection surface which is approximately at or below the lower plane of the ceiling to direct the air in a lateral pattern as it enters the room through the ceiling. It has been the practice to make the air deflecting member part of or in direct contact with the suspension member or the ceiling trim. This air deflecting member forms a ledge and must be made of a very thin sheet metal or the like which is substantially flush with the bottom surface of the ceiling or lower in order to get the proper discharge flow pattern. This results in a visible detail in the diffuser which may be architecturally or aesthetically undesirable. The deflection ledge width usually is 50% to 75% of the width of the discharge opening adding to the visible detail required of such a diffuser design. Such a diffuser is described, for example, in U.S. Pat. No. 3,406,623.